California Dam Spillway Repairs to Be Completed by Winter

California water officials said Wednesday that the $1.1 billion spillway at the nation’s tallest dam will be in full working order if it’s needed this winter, nearly two years after it was damaged and thousands were forced to flee.

Crews have finished pouring concrete on the main spillway at Oroville Dam, though it still needs to cure for a month and other work is necessary before it can be used, the California Department of Water Resources announced. Crews will also continue pouring concrete on an adjacent emergency spillway.

Both spillways at the dam, which is about 150 miles (240 kilometers) northeast of San Francisco, crumbled and fell away during heavy rains in early 2017, prompting fears of a catastrophic release of water. State officials had assured the public for days leading up to the failures that the dam could handle rising waters amid persistent and heavy rains.

Then on Feb. 12, 2017, officials ordered an immediate evacuation, fearing that a concrete weir that holds water in the lake could collapse within an hour.

The panic of the sudden evacuation turned into frustration and anger when many of the evacuees found themselves stuck in gridlocked traffic hours after fleeing the danger zone. Residents were allowed home a few days later after water behind the dam receded and the danger passed.

State officials promised to be done with concrete work by Nov. 1 so there would be enough time for it to dry and be used by December. With that goal met, crews will need to fill small holes left by the construction process, seal joints and place sand and rock outside the walls.

On the emergency spillway, crews have poured concrete to line a portion of a hillside to prevent a repeat of the erosion that caused the 2017 scare. They still need to pour more concrete to link that splash-pad with the concrete weir at the top.

“More than 700 construction workers … literally worked day and night to make incredible progress during the 2018 construction season,” Tony Meyers, project manager for the Department of Water Resources, said in a statement.

Officials said in September that the cost for reconstruction had ballooned to $1.1 billion and said the figure could still rise. The water agency plans to ask the Federal Emergency Management Agency to pay 75 percent of the repair costs after the project is finished. The rest would be borne by State Water Project customers, including massive Southern California water districts.

Last winter crews had a portion of the spillway rebuilt for the rainy season but were not able to use it at its full capacity. The water level was kept far below normal levels and it was never used.

With the spillway completely fully rebuilt, it can handle water flows up to 270,000 cubic feet per second (7,645 cubic meters per second), the maximum for which it was originally designed in the 1960s.

DWR officials said Wednesday they’ll again keep the water level low this winter to try and avoid using the spillway while work continues around it on the emergency spillway, site cleanup, road repair and other related projects.